Cut the pork into 1/4 to 1/2 inch pieces, slicing both parallel and perpendicular to the grain. Mix with garlic salt and soy sauce, massaging for 1 minute. Crack and beat the egg, mix with the pork for 30 seconds. Let the pork marinate while preparing the other ingredients.
Cut bell peppers, red onions, and pineapple into bite-sized pieces.
Make the sauce by mixing ketchup, brown sugar, vinegar, cornstarch, salt, and water until smooth.
Coat the pork with flour, massaging for 1-2 minutes. Add cornstarch to a plate and coat the pork pieces.
Heat oil in a wok to 300-350°F (149-176°C). Fry the pork for 7-8 minutes until browned. For a second fry, heat the oil to 400°F (204°C) and fry for 1-2 minutes. When the pork has cooked, drain on paper towel and set aside.
Stir-fry the vegetables for 30 seconds, then add the pineapple and cook for another 30 seconds. Remove from the wok. Reduce the sauce in the wok for 1-2 minutes.
Add everything back into the wok, toss with the sauce for 1-2 minutes. Serve immediately for crunchiness!